where "w" and "h" represent the width and heights of your photos, and "fps" means frames per second. fps=1 means 1 frame (photo) per second. if you want them to move slower, 0,5 would mean 1 frame/ 2 seconds, and so on.

you can play with the number of photos and fps value to make the file as long as the mp3 file.

i spent the best part of the last two days trying to master different programs like avidemux, kino, kdenlive, LiVES, images2mpeg etc. but this is what is so great about linux. some simple commands i found on the net.